A large epidemiological study of the genetic variation of barley yellow dwarf virus (BYDV) serotype PAV involving different host plant species was conducted. French BYDV PAV isolates were collected from barley and ryegrass, and their capsid protein gene sequences characterized using restriction fragment length polymorphism, single-strand conformation polymorphism, and sequence analyses. The data show that BYDV PAV isolates from five different continents are separated into two distinct groups named cpA and cpB, which are distributed irrespective of geographical location. Amino acid identity of the capsid proteins ranged from 93 to 99.5% in group cpA and from 95 to 99.5% in group cpB, while this value was only from 82 to 88% between the groups. Moreover, isolates from each group were found preferentially (up to 98%) in one of the two plant species examined. These results show that host plant species play a role in isolate selection and maintenance and that they contribute to the genetic diversity of BYDV PAV.